Length changes in PAN fibres during their pyrolysis to carbon fibres

A systematic study of the shrinkage taking place during the carbonization of polyacrylonitrile (PAN) fibres is reported. Shrinkage occurs from 200°C to 1000°C, the extent of which has been found to depend on (a) the time of preoxidation, (b) the type of oxidizing gas and (c) the carbonization conditions. The carbonization shrinkage is found to be independent of length changes during the preoxidation but can decrease from the usual 23% to about 2% by applying tension during the carbonization. A reaction is proposed to explain the shrinkage between 600°C and 800°C. The strength as well as Young's modulus of carbon fibres of under-oxidized fibres can be improved by applying tension during the carbonization. It is further predicted that the mechanical properties of carbon fibres preoxidized to the optimal level would decrease if carbonized under excessive tension.     

生物质热解炭化反应设备研究进展

生物质热解炭化技术作为生物质能源开发利用的一种重要途径,已经得到国内外广泛关注。文章介绍了生物质热解炭化反应设备的两大类型,即窑式炭化炉和固定床式热解炉。详细论述了各种典型设备的结构特点和适用范围,认为与窑式炭化炉相比,固定床式热解炭化炉炭化周期短、对生物质原料适应性和可操作性更强、产炭品质更有保障。最后指出了高效、稳定、机械化是生物质热解炭化设备未来的研究和发展方向。     

Optimization of stabilization and carbonization treatment of PAN fibres and structural characterization of the resulting carbon fibres

The properties of carbon fibres made from PAN are controlled by the heat treatment cycles during stabilization and carbonization. Optimum conditions can be derived by simple but time-consuming trials. The paper presents an indirect laboratory method, which is based on TMA and DSC measurements during the stabilization period. Results from this method contribute additionally to the explanation of the various simultaneously occurring chemical reactions, mainly dehydrogenation, intra- and intermolecular cyclization.Shrinkage measurements during stabilization under time linear heating show the start and end of the chemical stabilization reactions. The optimum stabilization conditions are derived from the shrinkage behavior as a function of the heating rate. As the stabilization is strongly affected by the heat of reaction, DSC measurements contribute to the accuracy but also to the explanation of the results from the TMA method.These stabilization conditions were applied for the preparation of carbon fibres which are characterized by mechanical and physical methods.     

Effect of carbonization time on the structure and electromagnetic parameters of porous-hollow carbon fibres

A series of polyacrylonitrile-based porous-hollow carbon fibres (PAN-PHCFs) were prepared by carbonizing PAN porous-hollow cured fibres at 1073 K for different times in nitrogen. The effects of carbonization time on the structure, electrical volume conductivity and electromagnetic parameters were investigated. Results indicate that the degree of graphitization increases as carbonization time increases. The electrical volume conductivity increases as the degree of graphitization and carbonization time increase. The real and imaginary parts of the complex permittivity (′ and ″) increase with carbonization time increasing. The values of ′ and ″ of composites of PAN-PHCFs and paraffin are 13.76 and 10.09 when the carbonization time is 240 min, and the electrical volume conductivity of PAN-PHCFs is 190.47 Ω⁻¹ m⁻¹.     

Oxidation and carbonization in the preparation of carbon fibres from petroleum pitch

Conclusions -- Gaseous and resinous products are evolved in the thermo-oxidation of spun pitch fibres. The main components of the gas are H₂O, CO, and CO₂. The effect of rate of temperature elevation, velocity of the air stream, and the duration and temperature of thermo-oxidation on the amount of evolved oxidation products, and oxygen content and sample weight gain have been investigated.-- The kinetics of evolution of H₂, CO, CH₄, and CO₂ has been studied in the carbonization of spun and oxidized pitch fibres. It has been shown that during temperature elevation CO₂ is initially evolved, and then CO and CH₄. H₂ is evolved at temperatures of 540°C and higher.Bashkirskii State University. Translated from Khimicheskie Volokna, No. 3, pp. 37–38, May–June, 1991.     

Effect of carbonization temperature on the structure and microwave absorbing properties of hollow carbon fibres

A series of polyacrylonitrile-based hollow carbon fibres (PAN-HCFs) were prepared by carbonizing polyacrylonitrile (PAN) hollow cured fibres at temperature ranging from 550 to 950 °C for 1 h in nitrogen. The effects of carbonization temperature on the structure, elemental compositions, surface electrical conductivity, electromagnetic parameters and reflectivity of PAN-HCFs were investigated. Results indicate that the obtained PAN-HCFs have not been graphitized and the C content and surface electrical conductivity increases as the carbonization temperature increases. The reflectivity of composites of PAN-HCFs and resin is −7.50 dB at 6.06 GHz and the band of the reflectivity under −5 dB is 6 GHz when the carbonization temperature is 750 °C.     

Polyethylene with low combustibility for construction applications containing chemical fibres and disperse fillers

The studies demonstrated the possibility of practical implementation of a method of fabricating difficultly combustible polyethylene by incorporating chlorinated paraffin stabilized with CaCO₃ and fireproof fibres in the polymer. The PCM based on the modified polyethylene have high physicomechanical characteristics and low combustibility, which places them in the class of construction materials for engineering and technical applications. Engels Engineering Institute, Saratov State Engineering University. Translated fromKhimicheskie Volokna, No. 6, pp. 46–49, November–December, 1999.     

Characteristics of the combustibility of fibre-forming polymers,fibres, and fibre materials (textiles)

The features of ignition, combustion, and the basic combustibility indexes of fibre-forming polymers, fibres, and fibre materials (textiles) are briefly analyzed. Data are reported on the basic combustibility indexes and their dependence on the type and chemical structure of the polymer. Ways of reducing the combustibility of fibres and fibre materials are briefly characterized. Data are reported on the basic types of difficultly combustible fibres and textiles. Special attention is focused on the products of pyrolysis and combustion with respect to their toxicity.     

Modification of the pyrolysis/carbonization of PPTA polymer by intermediate isothermal treatments

Pyrolysis/carbonization of poly (p-phenylene terephtalamide) (PPTA) was investigated, studying the possibility of modifying the pyrolysis/carbonization behavior and hence the carbon yield by introducing intermediate isothermal treatments. Thermogravimetric analysis (TG) was used to establish the main degradation steps of the material. It showed that the yield of solid residue at 950 °C increases by more than 15 wt.% by introducing an isothermal step at 500 °C for at least 50 min. Intermediate decomposition products at different temperatures/times of PPTA decomposition were characterized by X-ray diffraction (XRD), elemental microanalysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). XRD results showed that carbonization progresses during the isothermal step, so that the material is degraded loosing its crystallinity in a continuous way. DRIFTS spectra showed that PPTA undergoes a rupture of polymeric chains during the isothermal stage enhancing aryl nitrile formation. This favors crosslinking reactions that take place with increasing temperature, yielding a solid residue with a higher nitrogen content and higher char yield.     

生物质炭化热解气催化重整制取费-托合成气研究进展

生物质热解气是一种高热值的可燃气体,具有重要的开发利用价值,但由于其复杂的组分,多焦油和CO₂、CH₄等成分对热解气化过程以及相关的设备都有较大的危害,而冷凝下来形成的黏稠液体易造成管道堵塞,直接燃用产生的炭黑会造成环境污染,成为制约热解气进一步开发利用的主要因素。本文分析了热解气催化重整制取费-托合成气的可行性,分别介绍了连续和分段式热解-催化重整设备,镍基、钙基、铁基、碱金属类、生物炭等催化剂,以及热解气分离提纯技术等方面的研究现状,分析了目前热解气制取费-托合成气研究中存在的催化重整设备规格不统一、缺乏相关的行业标准、不同催化剂与催化剂助剂的催化重整效果、机理尚不明确等问题,并提出了采用分段式热解-催化重整设备,并以炭化产品生物炭作为催化重整催化剂的未来研究方向,开辟了生物质炭化热解气开发利用的新途径。     

Influence of elemental composition on carbonization pyrolysis of sporopollenin and lignite as models of kerogens

Two organic substances (sporopollenin and lignite) were heat-treated as models of kerogens and the resulting chars have been studied by electron microscopy, differential thermal analysis, thermogravimetry and IR spectroscopy.Sporopollenin (H/C = 1.56, O/C = 0.34) melts with decomposition at 436°C. Molecular orientation (1000 Å in extent) appears at 460°C after the weight loss rate maximum. It coincides with the aromatic CH maximum, the OH and carbonyl-carboxyl minima and comes before the aliphatic CH minimum and before the maximum spin concentration as well. Experimental conditions variations (quantity, pressure, action of oxygen) noticeably modify molecular orientation extension (from 50 Å to more than 2000 Å).During pyrolysis, lignite (H/C = 1.12, O/C = 0.44) does not melt and shows a small molecular orientation extension which unlike sporopollenin is not sensitive to experimental conditions. This behaviour is due to persistent oxygenated functions, some of them bonding the aromatic layer stacks.Sporopollenin preheat-treated in air (reticulation) appears comparable to lignite, which confirms the major part played by oxygen as far as melting and molecular orientation are concerned.     

The influence of pyrolysis on physical properties and microstructure of modified PAN fibers during carbonization

Modification of polyacrylonitrile (PAN) fibers with potassium permanganate has reduced the time required for stabilization and also improved the mechanical properties of the resulting carbon fibers. In this study, the effect of modification on the physical properties, microstructure, and elemental composition of fibers during the carbonization process was examined for the first time. The resulting carbon fibers developed from modified PAN fibers had a higher density, a greater stacking size (Lc), and a higher preferred orientation than those developed from unmodified PAN fibers. The carbon fibers developed from the modified PAN fibers also showed an improvement in tensile strength from 20 to 40%. These fibers showed a radial structure in the fracture surface and were somewhat different structurally in the cross section than were the carbon fibers developed from the original PAN fibers. A model for the structure of both carbon fibers is presented. The relationship between the formation of closed pores from open pores and the variety of cumulative pore area during the heat-treatment stage is also discussed.     

A study of pyrolysis of phenolic resin reinforced with carbon fibres and oxidized pan fibres

Pyrolysis of composites prepared from a phenol-formaldehyde resin and carbon fibres (CFRC) or oxidized PAN fibres (OFRC) has been investigated up to 1270 K. Two temperature regions can be distinguished in the pyrolysis of the CFRC: below 770 K the carbon fibres hold the composite structure resisting the tendency of the resin to produce composite shrinkage; above 770 K the CFRC volume and porosity abruptly increase due to a weakening of fibre/resin adhesion. During the pyrolysis of the OFRC a chemical reaction at the fibre/resin interface apparently takes place, beginning at 570 K and producing important changes in the material at 870–970 K. Somewhat smaller weight losses and markedly lesser shrinkage of the pyrolysed composite with respect to its separately treated components have been found. The fibres and the resin coalesce into a product having relatively high density and low porosity, the latter mainly consisting of narrow pores. Hydrogen content of the product is lower than that of the separately treated constituents. The reflections of both the resin and the oxidized PAN fibres are seen only in the X-ray patterns of the OFRC treated at low temperature, but above 670 K only the reflection due to the fibres appears. The interlayer spacing of the fibres in the composite is greater than in the fibres alone treated under the same conditions. According to the IR spectra, the CN groups and aromatic CH groups disappear from the composite at lower temperature than from its components treated separately.The existence of the reaction between the resin and the oxidized PAN fibres, leading to the destruction of the fibre materials, means that the co-carbonization product at 1270 K is not a composite and will not have the necessary mechanical properties. Therefore, this study must continue to look for fibres and matrices which are compatible during co-carbonization to 1270 K.     

Desulfurization of petroleum residues and their carbonization properties

The desulfurization of petroleum residues of high sulfur content was carried out using three kinds of Lewis acids under a nitrogen flow of atmospheric pressure at 150–330°C. Considerable amounts of sulfur were eliminated from the residue as hydrogen sulfide with the aid of aluminum chloride at 150°C or higher temperatures. Ferric or zinc chloride was found also to eliminate sulfur from the residue in the form of the corresponding metal sulfides at 330°C without the evolution of hydrogen sulfide.Effects of such desulfurization on the coking properties were observed by means of optical microscopy and X-ray diffraction. Although the original residues gave cokes with a mosaic arrangement of anisotropic domains, benzene-soluble fractions of the desulfurized residue gave a graphitizable needle coke. The desulfurized residues were further analyzed by chemical techniques to study the structural change brought about by acidic desulfurization. This kind of desulfurization was revealed to be carried out without decreasing the aromaticity of the residue, being different from the hydrodesulfurization with cobalt-molybdena catalysts.     

碳纤维用聚丙烯腈基预氧丝碳化裂解过程研究进展

综合论述了预氧丝在碳化裂解过程中的物理化学变化,包括裂解气体及化学反应、纤维物理收缩和应力变化、组织结构变化及碳化工艺对碳纤维性能的影响,并对聚丙烯腈基预氧丝的碳化研究前景进行了展望.     

Dependence of acoustical characteristics on molecular orientation and strength of man-made fibres

Conclusions A correlative connection has been established between acoustical characteristics and the orientation of macromolecules or the strength of yarns of various chemical natures.It has been shown that any structural transformations in oriented polymers which lead to a change in molecular orientation cause a change in the absorption coefficient of ultrasonic waves.Translated from Khimicheskie Volokna, No. 5, pp. 26–28, September–October, 1984.